6 Analyzing Garbage Collection Data

HPjmeter allows you to process garbage collection (GC) data from Java virtual machines.

Separating the GC data collection step from the analysis step has the following advantages:

•The data analysis can be done at a different time and on a different platform than was used to run the application. For example, it can be done on a desktop system or on a laptop.

•A non-interactive agent will often impose less overhead than an interactive one.

•The data files obtained naturally facilitate comparison of different runs or creation of a history of performance improvements.

For detailed analysis of the efficiency of garbage collection, it is useful to take a close look at garbage collection patterns. A study of patterns of garbage collection can help you determine whether or not the best GC type and heap size are being applied appropriately during the application run. You can also use detailed GC data to uncover problems in the application programming.

With the collection of verbose GC data, HPjmeter is able to present extensive details about the memory usage and garbage collection (GC) exhibited when an application is running. Details are presented in a data summary and in graphic visualizers that can be adjusted to focus on particular aspects of the data.

Obtaining Garbage Collection Data

The -Xverbosegcoption, available for the HP-UX HotSpot™ VM, was specifically designed to produce ASCII garbage collection data files for in-depth analysis using HPjmeter.

-Xloggccan be useful for quick comparison of garbage collection behavior across different platforms.

The GC viewer automatically opens when you open an Xverbosegc or Xloggc file from the HPjmeter console.

Data Collection with -Xverbosegc

-Xverbosegcproduces detailed information about the performance of individual garbage collector types for the entire Java application.

To run your application with an option to capture the garbage collection information, use the following command:

$ java ... -Xverbosegc[01][:file=[stdoutstderrfilename[,[n][h][d][u][t]]]]

The following table lists examples of supported -Xverbosegcoptions for capturing garbage collection data. This table provides information for Java 1.5.0.04. Other versions may differ from this. HPjmeter correctly presents and labels collected data based on the Java version running with the application. To see the complete list of available options for the Java version you are running, use

$ java ... -Xverbosegc:help

To see the availability of HPjmeter metrics from -Xverbosegcdata collection, see -Xverbosegc and -Xloggc Options and Their Corresponding Metrics (page 85).

Table 6-1 Supported -Xverbosegcoptions for Java 1.5.0.04

01

0 prints after every old generation garbage collection or after a full GC.

 

1 prints after every garbage collection (default).

:file=[stdoutstderrfilename] stderr (default) directs output to standard error stream. stdout directs output to standard output stream.

80 Analyzing Garbage Collection Data